Reflective mask blank, reflective mask, method of manufacturing reflective mask blank, and method of manufacturing reflective mask

ABSTRACT

A reflective mask blank includes a substrate; a multilayer reflective film that reflects EUV light; and a phase shift film that shifts a phase of the EUV light, in this order. The phase shift film contains a compound containing ruthenium (Ru) and an element X2 different from Ru. A melting point MP1 of an oxide of the compound and a melting point MP2 of a fluoride or an oxyfluoride of the compound satisfy a relation of 
       0.625 MP1+MP2≤1000.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of InternationalApplication No. PCT/JP2022/030631, filed Aug. 10, 2022, which claimspriority to Japanese Patent Application No. 2021-138856 filed Aug. 27,2021. The contents of these applications are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The disclosure herein generally relates to a reflective mask blank, areflective mask, a method of manufacturing a reflective mask blank, anda method of manufacturing a reflective mask.

2. Description of the Related Art

Along with the recent miniaturization of semiconductor devices, EUVlithography (EUVL), an exposure technology using Extreme Ultra-Violet(EUV) light, has been developed. The EUV light includes a soft X-ray anda vacuum ultraviolet light, and specifically has a wavelength of from0.2 nm to 100 nm. At present, EUV light with a wavelength of about 13.5nm is mainly studied.

In the EUVL, a reflective mask is used. The reflective mask includes asubstrate, such as a glass substrate, a multilayer reflective filmformed on the substrate, and a phase shift film formed on the multilayerreflective film. An opening pattern is formed in the phase shift film.In the EUVL, the opening pattern of the phase shift film is transferredto a target substrate, such as a semiconductor substrate. Thetransferring includes transferring a reduced opening pattern.

The phase shift film of Example 1 of Japanese Patent No. 5233321contains a compound in which a composition ratio between Ta and Ru is2:1. The phase shift film of Example 2 of Japanese Patent No. 5233321contains a compound in which a composition ratio among Ta, N, and Ru is2:2:1.

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Conventionally, a chemical composition and a structure of the phaseshift film for the EUVL have been studied.

An aspect of the present disclosure provides a technique for lowering arefractive index of a phase shift film and improving processability ofthe phase shift film.

Means for Solving the Problem

According to an aspect of the present disclosure, a reflective maskblank includes a substrate; a multilayer reflective film that reflectsEUV light; and a phase shift film that shifts a phase of the EUV light,in this order. The phase shift film contains a compound containing Ruand an element X2 different from Ru. A melting point MP1 of an oxide ofthe compound and a melting point MP2 of a fluoride or an oxyfluoride ofthe compound satisfy a formula (1).

[Equation 1]

0.625 MP1+MP2≤1000   (1)

Effects of the Invention

According to an aspect of the present disclosure, by forming the phaseshift film with the Ru compound satisfying the above formula (1), it ispossible to lower the refractive index of the phase shift film andimprove the processability of the phase shift film.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present disclosure will beapparent from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view showing a reflective mask blankaccording to an embodiment;

FIG. 2 is a cross-sectional view showing a reflective mask according tothe embodiment;

FIG. 3 is a cross-sectional view of the reflective mask for illustratingan example of EUV light reflected by the reflective mask of FIG. 2 ;

FIG. 4 is a cross-sectional view showing a reflective mask blankaccording to a variation of the embodiment;

FIG. 5 is a cross-sectional view showing a reflective mask according tothe variation of the embodiment;

FIG. 6 is a diagram showing a relationship among melting points MP1 andMP2 shown in TABLE 1, a formula (1), and a formula (2);

FIG. 7 is a flowchart showing a method of manufacturing the reflectivemask blank according to the embodiment;

FIG. 8 is a flowchart showing a method of manufacturing the reflectivemask according to the embodiment; and

FIG. 9 is a diagram showing an example of a relationship between anetching rate for the Ru compound by a mixture gas of a Cl₂ gas and an O₂gas and a ratio of an element X2 to the Ru compound.

DESCRIPTION OF THE EMBODIMENT

In the following, embodiments of the present disclosure will bedescribed with reference to the accompanying drawings. In each drawing,to the same or corresponding configurations, the same reference numeralwill be assigned, and an explanation may be omitted. In thespecification, a symbol “-” representing a numerical range indicatesthat values before and after the symbol are included as a lower limitvalue and an upper limit value, respectively.

In FIGS. 1 to 5 , an X-axis direction, a Y-axis direction, and a Z-axisdirection are directions orthogonal to each other. The Z-axis directionis a direction perpendicular to a first main surface 10 a of a substrate10. The X-axis direction is a direction perpendicular to an incidentplane of EUV light (a plane including an incident light beam and areflected light beam). As shown in FIG. 3 , when viewed from the X-axisdirection, the incident light beam and the reflected light beam areinclined towards the Y-axis direction on propagating in the Z-axisdirection. That is, as shown in FIG. 3 , the incident light beam isinclined towards the Y-axis positive direction on propagating in theZ-axis negative direction, and the reflected light beam is inclinedtowards the Y-axis positive direction on propagating in the Z-axispositive direction.

A reflective mask blank 1 according to an embodiment will be describedwith reference to FIG. 1 . The reflective mask blank 1 includes, forexample, the substrate 10; a multilayer reflective film 11; a protectionfilm 12; a phase shift film 13; and an etching mask film 14, in thisorder. The multilayer reflective film 11, the protection film 12, thephase shift film 13, and the etching mask film 14 are formed in thisorder on the first main surface 10 a of the substrate 10. The reflectivemask blank 1 only needs to have at least the substrate 10, themultilayer reflective film 11, and the phase shift film 13.

The reflective mask blank 1 may further have a functional film, which isnot shown in FIG. 1 . For example, the reflective mask blank 1 may havea conductive film on the side opposite to the multilayer reflective film11 with respect to the substrate 10. The conductive film may be used,for example, to attract a reflective mask 2 to an electrostatic chuck ofan exposure apparatus. The reflective mask blank 1 may have a diffusionbarrier film (not shown) between the multilayer reflective film 11 andthe protection film 12. The diffusion barrier film prevents metalelements contained in the protection film 12 from diffusing into themultilayer reflective film 11.

As shown in FIG. 4 , the reflective mask blank 1 may have a buffer film15 between the protection film 12 and the phase shift film 13. Thebuffer film 15 protects the protection film 12 from an etching gas forforming an opening pattern 13 a in the phase shift film 13. The bufferfilm 15 is etched more gently than the phase shift film 13. Finally, thebuffer film 15 has the same opening pattern as the opening pattern 13 aof the phase shift film 13 as shown in FIG. 5 .

Next, the reflective mask 2 according to the embodiment will bedescribed with reference to FIGS. 2 and 3 .

The reflective mask 2 is manufactured using, for example, the reflectivemask blank 1 shown in FIG. 1 , and includes the opening pattern 13 a inthe phase shift film 13. The etching mask film 14 shown in FIG. 1 isremoved after the opening pattern 13 a is formed in the phase shift film13.

In EUVL, the opening pattern 13 a of the phase shift film 13 istransferred to a target substrate, such as a semi-conductor substrate.The transferring includes transferring a reduced opening pattern. In thefollowing, the substrate 10, the multilayer reflective film 11, theprotection film 12, the phase shift film 13, and the etching mask film14 will be described in this order.

The substrate 10 is, for example, a glass substrate. A material of thesubstrate 10 is preferably quartz glass containing TiO₂. Compared withgeneral soda lime glass, a linear expansion coefficient of the quartzglass is small, and thereby a dimensional change due to a temperaturechange is small. The quartz glass may contain 80 mass %-95 mass % ofSiO₂ and 4 mass %-17 mass % of TiO₂. When the TiO₂ content is 4 mass%-17 mass %, the linear thermal expansion coefficient around roomtemperature is substantially zero, and almost no dimensional changearound room temperature occurs. The quartz glass may contain a thirdcomponent or impurity other than SiO₂ and TiO₂. The material of thesubstrate 10 may be crystallized glass in which a β-quartz solidsolution is precipitated, silicon, metal, or the like.

The substrate 10 has the first main surface 10 a and a second mainsurface 10 b opposite to the first main surface 10 a. The multilayerreflective film 11 and the like are formed on the first main surface 10a. The size of the substrate 10 in a plan view (viewed in the Z-axisdirection) is, for example, 152 mm longitudinally and 152 mm laterally.The longitudinal and lateral dimensions may be greater than or equal to152 mm. Each of the first main surface 10 a and the second main surface10 b has, for example, a square-shaped quality-guaranteed region at thecenter thereof. The size of the quality-guaranteed region is, forexample, 142 mm longitudinally and 142 mm laterally. Thequality-guaranteed region on the first main surface 10 a preferably hasa root mean square roughness Rq of 0.15 nm or less and a flatness of 100nm or less. The quality-guaranteed region of the first main surface 10 ais preferably free from a defect that may cause a phase defect.

The multilayer reflective film 11 reflects EUV light. The multilayerreflective film 11 is formed by alternately stacking, for example, ahigh refractive index layer and a low refractive index layer. A materialof the high refractive index layer is, for example, silicon (Si), and amaterial of the low refractive index layer is, for example, molybdenum(Mo). With this combination, the multilayer reflective film is a Mo/Simultilayer reflective film. In addition, a Ru/Si multilayer reflectivefilm, a Mo/Be multilayer reflective film, a Mo compound/Si compoundmultilayer reflective film, a Si/Mo/Ru multilayer reflective film, aSi/Mo/Ru/Mo multilayer reflective film, a Si/Ru/Mo/Ru multilayerreflective film, or the like can also be used as the multilayerreflective film 11.

The film thickness of each layer constituting the multilayer reflectivefilm 11 and the number of repeating units of layers can be appropriatelyselected according to the material of each layer and a reflectance toEUV light. When the multilayer reflective film 11 is a Mo/Si multilayerreflective film, in order to achieve a reflectance of 60% or more withrespect to EUV light having an incident angle θ (see FIG. 3 ) of 6°, aMo layer having a film thickness of 2.3±0.1 nm and a Si layer having afilm thickness of 4.5±0.1 nm may be stacked so that the number ofrepeating units is 30 or more and 60 or less. The multilayer reflectivefilm 11 preferably has the reflectance of 60% or more to EUV light at anincident angle θ of 6°. The reflectance is more preferably 65% or more.

The method of forming each layer constituting the multilayer reflectivefilm 11 is, for example, a DC sputtering method, a magnetron sputteringmethod, or an ion beam sputtering method. For example, film formationconditions for each of the Mo layer and the Si layer, when a Mo/Simultilayer reflective film is formed by the ion beam sputtering method,will be shown as follows.

Film Formation Condition for Si Layer

Target: Si;

Sputtering gas: Ar;

Gas pressure: 1.3×10⁻² Pa-2.7×10⁻² Pa;

Ion acceleration voltage: 300 V-1500 V;

Film formation rate: 0.030 nm/sec-0.300 nm/sec; and

Film thickness of Si layer: 4.5±0.1 nm.

Film Formation Condition for Mo Layer

Target: Mo;

Sputtering gas: Ar;

Gas pressure: 1.3×10⁻² Pa-2.7×10⁻² Pa;

Ion acceleration voltage: 300 V-1500 V;

Film formation rate: 0.030 nm/sec-0.300 nm/sec; and

Film thickness of Mo layer: 2.3±0.1 nm

Repeating Unit of Si layer and Mo Layer

Number of repeating units: 30-60 (preferably 40-50).

The protection film 12 is formed between the multilayer reflective film11 and the phase shift film 13, to protect the multilayer reflectivefilm 11 from the etching gas. The etching gas is used to form theopening pattern 13 a (see FIG. 2 ) in the phase shift film 13. Theetching gas is, for example, a mixed gas of a fluorine-based gas and anoxygen-based gas.

The fluorine-based gas is, for example, a CF₄ gas, a CHF₃ gas, a SF₆gas, a BF₃ gas, a XeF₂ gas, or a mixture of these gases. Theoxygen-based gas is, for example, an O₂ gas, an O₃ gas, a CO₂ gas, a NO₂gas, a SO₂ gas, a H₂O gas, or a mixture gas thereof. A volume ratiobetween the oxygen-based gas and the fluorine-based gas, (oxygen-basedgas):(fluorine-based gas), is preferably 10:90-50:50, more preferably20:80-40:60.

A ratio (ER2/ER1) of an etching rate ER1 of etching the phase shift film13 using the etching gas to an etching rate ER2 of etching theprotection film 12 using the etching gas is also referred to as a firstselection ratio. The higher the first selection ratio is, the better theprocessability of the phase shift film 13 is.

When the buffer film 15 is not present between the protection film 12and the phase shift film 13 as shown in FIGS. 1 and 2 , the firstselection ratio is preferably 10 or more, and more preferably 30 ormore. The first selection ratio is preferably 200 or less, and morepreferably 100 or less.

When the buffer film 15 is not present, the protection film 12preferably contains rhodium (Rh). Alternatively, the protection filmpreferably contains 50 at % or more of Rh and at least one element X1selected from the group consisting of ruthenium (Ru), silicon (Si),aluminum (Al), hafnium (Hf), yttrium (Y), tantalum (Ta), niobium (Nb),molybdenum (Mo), and iridium (Ir). According to the above-describedcontents, the first selection ratio can be made 10 or more.

In the case where the protection film 12 contains Ru, Nb, Mo, or Y, anextinction coefficient of the protection film 12 can be reduced withoutgreatly increasing the refractive index of the protection film 12, sothat the reflectance for EUV light can be improved. When the protectionfilm 12 contains Ru, Ta, Ir, or Y, resistance to the etching gas andresistance to a sulfuric acid-hydrogen peroxide mixture can be improved.The element X1 is preferably Ru, Nb, Mo, or Y.

An element ratio between the element X1 and rhodium (Rh), X1:Rh, ispreferably 1:99-1:1. In the specification of the present application,the element ratio means a molar ratio. When the value of the ratio X1/Rhis 1/99 or more, the reflectance for EUV light is excellent. When thevalue of the ratio X1/Rh is less than or equal to 1, the resistance ofthe protection film 12 to the etching gas is excellent. The elementratio between X1 and Rh, X1:Rh, is more preferably 3:10-1:1.

The protection film 12 may contain, in addition to rhodium (Rh), atleast one element Y1 selected from the group consisting of nitrogen (N),oxygen (O), carbon (C), and boron (B). Although the element Y1 reducesthe resistance of the protection film 12 to the etching gas, the elementY1 improves the smoothness of the protection film 12 according toreduction of crystallinity of the protection film 12. The protectionfilm 12 containing the element Y1 has a non-crystalline structure or amicrocrystalline structure. When the protection film 12 has anon-crystalline structure or a microcrystalline structure, the X-raydiffraction profile of the protection film 12 does not exhibit a clearpeak.

When the protection film 12 contains Y1 in addition to Rh, it ispreferable that the content of Rh or the total content of Rh and X1 is40 at %-99 at %, and the total content of Y1 is 1 at %-60 at %. When theprotection film 12 contains Y1 in addition to Rh, it is more preferablethat the content of Rh or the total content of Rh and X1 is 80 at %-99at %, and the total content of Y1 is 1 at %-20 at %.

When the protection film 12 contains 90 at % or more of Rh, contains X1,Y1, or both, and has a film density of 10.0 g/cm³-14.0 g/cm³, theprotection film 12 has a non-crystalline structure or a microcrystallinestructure. The film density of the protection film 12 is preferably 11.0g/cm³-13.0 g/cm³. When the protection film 12 contains 100 at % of Rhand has the film density of 11.0 g/cm³-12.0 g/cm³, the protection film12 has a non-crystalline structure or a microcrystalline structure. Thefilm density of the protection film 12 is measured using an X-rayreflectance method.

When the buffer film 15 is present between the protection film 12 andthe phase shift film 13 as shown in FIGS. 4 and 5 , the first selectionratio only needs to be greater than 1.0, and the protection film 12 maybe, for example, a Ru film or a SiO film. When the protection film 12 isa Ru film or a SiO film, the first selection ratio is less than 3.0.

In the case where the buffer film 15 is present, the processability ofthe phase shift film 13 is expressed by a second selection ratio, whichwill be described below. The second selection ratio is a ratio of theetching rate ER1 of etching the phase shift film 13 using the etchinggas to an etching rate ER3 of etching the buffer film 15 using theetching gas, i.e., ER3/ER1. The higher the second selection ratio is,the better the processability of the phase shift film 13 is. The secondselection ratio is preferably 3.0 or more. The second selection ratio ispreferably 200 or less, and more preferably 100 or less.

The buffer film 15 preferably contains tantalum (Ta). Alternatively, thebuffer film preferably contains, in addition to Ta, at least one elementselected from the group consisting of oxygen (O) and nitrogen (N). Whenthe buffer film 15 contains tantalum nitride (TaN) or tantalumoxynitride (TaON), the second selection ratio is 3.0 or more, which willbe described in detail in the section of Examples.

The film thickness of the buffer film 15 is preferably 1.0 nm or moreand 10 nm or less. When the film thickness of the buffer film 15 is 1.0nm or more, the buffer film 15 can protect the protection film 12. Whenthe film thickness of the buffer film 15 is 10 nm or less, the filmthickness of the phase shift film 13 can be increased while suppressingan increase in a shadowing effect, which will be described below, andthereby a sufficient phase shift effect can be obtained.

The description returns to the protection film 12. The protection film12 has resistance to sulfuric acid-hydrogen peroxide mixture (SPM),which is a cleaning liquid, and protects the multilayer reflective film11 from the sulfuric acid-hydrogen peroxide mixture. The sulfuricacid-hydrogen peroxide mixture is used, for example, to remove a resistfilm (not shown) or to clean the reflective mask 2. The resist film isformed on the etching mask film 14 (or on the phase shift film 13 whenthe etching mask film 14 is not present).

The film thickness of the protection film 12 is preferably 1.0 nm ormore and 10.0 nm or less, and more preferably 2.0 nm or more and 3.5 nmor less.

The root mean square roughness Rq of the protection film 12 ispreferably 0.3 nm or less, and more preferably 0.1 nm or less.

The method of forming the protection film 12 includes, for example, a DCsputtering method, a magnetron sputtering method, or an ion beamsputtering method. For example, film formation conditions, when a Rhfilm is formed by the DC sputtering method, will be shown as follows.

Film Formation Conditions for Rh Film

Target: Rh;

Sputtering gas: Ar;

Gas pressure: 1.0×10⁻² Pa-1.0×10⁰ Pa;

Input power density per unit area of target: 1.0 W/cm²-8.5 W/cm²;

Film formation rate: 0.020 nm/sec-1.000 nm/sec; and

Film thickness of Rh film: 1 nm-10 nm.

When the Rh film is formed, a N₂ gas or a mixture gas of an Ar gas and aN₂ gas may be used as the sputtering gas. The volume ratio of a N₂ gasin the sputtering gas, N₂/(Ar+N₂), is 0.05 or more and 1.0 or less.

For example, film formation conditions, when a RhO film is formed by theDC sputtering method, will be shown as follows.

Film Formation Conditions for RhO Film

Target: Rh;

Sputtering gas: an O₂ gas, or a mixture gas of an Ar gas and an O₂ gas;

Volume ratio of an O₂ gas in sputtering gas, O₂/(Ar+O₂)): 0.05-1.0;

Gas pressure: 1.0×10⁻² Pa-1.0×10⁰ Pa;

Input power density per unit area of target: 1.0 W/cm²-8.5 W/cm²;

Film formation rate: 0.020 nm/sec-1.000 nm/sec; and

Film thickness of RhO film: 1 nm-10 nm.

For example, film formation conditions, when a RhRu film is formed bythe DC sputtering method, will be shown as follows.

Film Formation Conditions for RhRu Film

Target: Rh and Ru (or RhRu);

Sputtering gas: Ar;

Gas pressure: 1.0×10⁻² Pa-1.0×10⁰ Pa;

Input power density per unit area of target: 1.0 W/cm²-8.5 W/cm²;

Film formation rate: 0.020 nm/sec-1.000 nm/sec; and

Film thickness of RhRu film: 1 nm-10 nm.

The phase shift film 13 is a film in which the opening pattern 13 a isto be formed. The opening pattern 13 a is not formed in themanufacturing process of the reflective mask blank 1 but is formed inthe manufacturing process of the reflective mask 2. The phase shift film13 shifts a phase of second EUV light L2 with respect to a phase offirst EUV light L1 shown in FIG. 3 .

The first EUV light L1 is light that entered and passed through theopening pattern 13 a without passing through the phase shift film 13,was reflected by the multilayer reflective film 11, and passed throughthe opening pattern 13 a without passing through the phase shift film 13again and exited. The second EUV light L2 is light that entered andpassed through the phase shift film 13 while being absorbed by the phaseshift film 13, was reflected by the multilayer reflective film 11, andpassed through the phase shift film 13 while being absorbed again by thephase shift film 13 and exited.

The phase shift, which is greater than or equal to zero, between thefirst EUV light L1 and the second EUV light L2 is, for example,200°-250°. The phase of the first EUV light L1 may be advanced orretarded from the phase of the second EUV light L2. The phase shift film13 improves a contrast of a transferred image by utilizing aninterference between the first EUV light L1 and the second EUV light L2.The transferred image is an image obtained by transferring the openingpattern 13 a of the phase shift film 13 to a target substrate.

As the film thickness of the phase shift film 13 becomes smaller, aprojection effect (shadowing effect) is reduced. The shadowing effectmeans that, for example, as shown in FIG. 3 , a region that shields EUVlight due to a non-zero incident angle (e.g., 6°) appears near anopening edge of the opening pattern 13 a on the surface of the phaseshift film 13, and the size of the transferred image deviates from thedesired size. The smaller the film thickness of the phase shift film 13is, the better the processing accuracy of the opening pattern 13 a is.

In order to reduce the projection effect, the film thickness of thephase shift film 13 is, for example, 50 nm or less, preferably 45 nm orless, and more preferably 35 nm or less. In order to secure the phasedifference between the first EUV light L1 and the second EUV light L2,the film thickness of the phase shift film 13 is preferably 15 nm ormore, and more preferably 20 nm or more.

In order to reduce the film thickness of the phase shift film 13 so asto reduce the projection effect while securing the phase differencebetween the first EUV light L1 and the second EUV light L2, it iseffective to reduce the refractive index of the phase shift film 13, andit is effective that the phase shift film 13 contains ruthenium (Ru).The refractive index of Ru alone is 0.893. However, Ru decreases thefirst selection ratio and the second selection ratio. As a result, theprocessability of the phase shift film 13 may deteriorate.

The inventors of the present application studied a Ru compound as amaterial of the phase shift film 13. The Ru compound is generally etchedusing a mixture gas of a chlorine-based gas and an oxygen-based gas, forexample, a mixture gas of a Cl₂ gas and an O₂ gas. The inventors of thepresent application examined the relationship between an etching ratefor the Ru compound by the mixture gas of a Cl₂ gas and an O₂ gas andthe ratio of an element X2 to the Ru compound. The element X2 is anelement different from Ru, and is, for example, a metallic element or ametalloid element.

FIG. 9 shows an example of the relationship between the etching rate forthe Ru compound by the mixture gas of a Cl₂ gas and an O₂ gas and theratio of the element X2 to the Ru compound. The etching rate for the Rucompound was normalized by an etching rate for Ru alone. As the ratio ofthe element X2 to the Ru compound increases, the etching rate for the Rucompound decreases. Thus, the etching rate could not be increased byusing the Ru compound instead of Ru alone.

Next, the inventors of the present application studied etching of the Rucompound by using a mixed gas of a fluorine-based gas and anoxygen-based gas. The fluorine-based gas removes the Ru compound byfluorinating the Ru compound and volatilizing the fluoride. Theoxygen-based gas removes the Ru compound by oxidizing the Ru compoundand volatilizing the oxide. The fluorine-based gas and the oxygen-basedgas remove the Ru compound by fluorinating, oxidizing, oroxyfluorinating the Ru compound and volatilizing the fluoride, oxide, oroxyfluoride.

The inventors of the present application focused on a melting point MP1of an oxide of a Ru compound and a melting point MP2 of a fluoride or anoxyfluoride of a Ru compound. It is considered that the lower themelting point MP1, the more easily the oxide volatilizes and the higherthe etching rate becomes. Similarly, it is considered that the lower themelting point MP2 is, the more easily the fluoride or oxyfluoride isvolatilized and the higher the etching rate becomes. Since thevolatilization of the oxyfluoride occurs preferentially to thevolatilization of the fluoride, the melting point of the oxyfluoride isadopted as the melting point MP2 when the oxyfluoride is generated.

As will be described in detail in EXAMPLES, the inventors of the presentapplication have found through experiments that the etching rate for thephase shift film 13 can be increased and the processability of the phaseshift film 13 can be improved by forming the phase shift film 13 with aRu compound having melting points MP1 and MP2 satisfying the followingformula (1).

[Equation 2]

0.625 MP1+MP2≤1000   (1)

Moreover, as will be described in detail in EXAMPLES, the inventors ofthe present application have found through experiments that the etchingrate for the phase shift film 13 can be further increased and theprocessability of the phase shift film 13 can be further improved byforming the phase shift film 13 with a Ru compound having melting pointsMP1 and MP2 satisfying both the above formula (1) and the followingformula (2).

[Equation 3]

−0.500 MP1+MP2≤400   (2)

FIG. 6 shows relationships between pairs of the melting points MP1 andMP2, and the formula (1), and a relationship between the pairs and theformula (2). The pairs of the melting points will be shown in TABLE 1 inEXAMPLES. In FIG. 6 , a straight-line L represents a boundary between aregion where the formula (1) is satisfied and a region where the formula(1) is not satisfied. Examples 2, 3, 5 to 17, 21, 24, and 25 areexamples of the Ru compound that satisfies the formula (1). On the otherhand, Examples 4, 18 to 20, and 22 to 23 are examples of the Ru compoundthat does not satisfy the formula (1). Note that Example 1 is an exampleof Ru alone.

In FIG. 6 , a straight-line LA represents a boundary between a regionwhere the above-described formula (2) is satisfied and a region wherethe above-described formula (2) is not satisfied. Examples 2, 3, 5 to 8,10 to 12, 14 to 16, 24, and 25 are examples of the Ru compound thatsatisfies both the formula (1) and the formula (2). On the other hand,Examples 9, 13, 17, and 21 are examples of the Ru compound thatsatisfies the formula (1) but does not satisfy the formula (2).

The phase shift film 13 contains a compound containing Ru and X2. Theelement X2 is an element different from Ru, and is, for example, ametallic element or a metalloid element. The phase shift film 13preferably contains at least one element selected from the groupconsisting of Ta, W, Re, and Cr as the element X2. The phase shift film13 more preferably contains at least one element selected from the groupconsisting of Ta, W, and Re as the element X2.

When the phase shift film 13 contains Ta as the element X2, an elementratio between Ta and Ru (Ta:Ru) is, for example, 1:99-1:1. When theelement ratio Ta:Ru is 1:99-1:1, the above formula (1) is satisfied, andan etching rate higher than that of Ru alone is obtained. When a valueof the ratio (Ta/Ru) is 1/1 or less, a RuTa film having a refractiveindex of 0.925 or less and high resistance to a sulfuric acid-hydrogenperoxide mixture can be obtained. When the value of the ratio (Ta/Ru) isless than 1/99, an etching rate higher than that of Ru cannot beobtained. When the value of the ratio (Ta/Ru) is 52/48 or more, a RuTafilm having a refractive index of 0.926 or more is obtained. The elementratio between Ta and Ru (Ta:Ru) is preferably 1:99-1:1, more preferably5:95-1:1, and even more preferably 1:9-1:1.

When the phase shift film 13 contains W as the element X2, the elementratio between W and Ru (W:Ru) is, for example, 1:99-1:1. When theelement ratio W:Ru is 1:99-1:1, the above formula (1) is satisfied, andan etching rate higher than that of Ru alone is obtained. When a valueof the ratio (W/Ru) is 1/1 or less, a RuW film having a refractive indexof 0.925 or less and high resistance to a sulfuric acid-hydrogenperoxide mixture can be obtained. The element ratio between W and Ru(W:Ru) is preferably 1:99-1:1, more preferably 5:95-1:1, and even morepreferably 1:9-1:1.

When the phase shift film 13 contains Re as the element X2, the elementratio between Re and Ru (Re:Ru) is, for example, 1:99-1:1. When theelement ratio Re:Ru is 1:99-1:1, the above formula (1) is satisfied, andan etching rate higher than that of Ru alone is obtained. When a valueof the ratio (Re/Ru) is 1/1 or less, a RuRe film having a refractiveindex of 0.925 or less and high resistance to a sulfuric acid-hydrogenperoxide mixture can be obtained. The element ratio between Re and Ru(Re:Ru) is preferably 1:99-1:1, more preferably 5:95-1:1, and even morepreferably 1:9-1:1.

When the phase shift film 13 contains Cr as the element X2, the elementratio between Cr and Ru (Cr:Ru) is, for example, 1:99-4:1. When theelement ratio Cr:Ru is 1:99-4:1, the above formula (1) is satisfied, andan etching rate higher than that of Ru alone is obtained. When a valueof the ratio (Cr/Ru) is 4/1 or less, a RuCr film having a refractiveindex of 0.925 or less and high resistance to a sulfuric acid-hydrogenperoxide mixture can be obtained. When the value of the ratio (Cr/Ru) isless than 1/99, an etching rate higher than that of Ru cannot beobtained, and when the value of the ratio (Cr/Ru) is 83/17 or more, aRuCr film having a refractive index of 0.926 or more is obtained. Theelement ratio between Cr and Ru (Cr:Ru) is preferably 1:99-4:1, morepreferably 5:95-4:1, even more preferably 5:95-42:58, and particularlypreferably 1:9-42:58.

The phase shift film 13 may contain, in addition to Ru and X2, at leastone element Y2 selected from the group consisting of B, C, O, and N. Forexample, the phase shift film 13 may contain RuTaN. The phase shift film13 is not particularly limited, but may contain, for example, 0.01 at%-59 at % of the element Y2.

The refractive index n of the phase shift film 13 is, for example, 0.925or less, preferably 0.920 or less, more preferably 0.910 or less, andeven more preferably 0.90 or less. The refractive index n is preferably0.885 or more. In the specification of the present application, therefractive index is a refractive index for light with a wavelength of13.5 nm.

An extinction coefficient k of the phase shift film 13 is, for example,0.024 or more, preferably 0.030 or more, and more preferably 0.035 ormore. Further, the extinction coefficient k is preferably 0.065 or less.In the specification of the present application, the extinctioncoefficient is an extinction coefficient for light with a wavelength of13.5 nm.

As the optical characteristics (refractive index n and extinctioncoefficient k) of the phase shift film 13, values found in the databaseprovided by the Center for X-Ray Optics, Lawrence Berkeley NationalLaboratory, or values calculated from the “dependency on incident angle”of reflectance, which will be described later, are used.

An incident angle θ of EUV light, reflectance R with respect to the EUVlight, refractive index n of the phase shift film 13, and the extinctioncoefficient k of the phase shift film 13 satisfy the following formula(3).

$\begin{matrix}\left\lbrack {{Equation}4} \right\rbrack &  \\{R = {{❘\frac{{\sin\theta} - \left( {\left( {n + {ik}} \right)^{2} - {\cos^{2}\theta}} \right)^{1/2}}{{\sin\theta} + \left( {\left( {n + {ik}} \right)^{2} - {\cos^{2}\theta}} \right)^{1/2}}❘}.}} & (3)\end{matrix}$

Measurements were performed for a plurality of combinations of theincident angle θ and the reflectance R, and the refractive index n andthe extinction coefficient k were calculated by the least-squares methodso that a sum of errors between the measured data and values obtainedusing the formula (3) was minimized.

The etching rate for the phase shift film 13 with sulfuric acid-hydrogenperoxide mixture is 0 nm/min-0.05 nm/min. A sulfuric acid-hydrogenperoxide mixture is used for removing a resist film, cleaning thereflective mask 2, or the like. When the etching rate for the phaseshift film 13 with sulfuric acid-hydrogen peroxide mixture is 0.05nm/min, damage to the phase shift film 13 during cleaning can besuppressed.

The method of forming the phase shift film 13 includes, for example, aDC sputtering method, a magnetron sputtering method, or an ion beamsputtering method.

The etching mask film 14 is formed on the phase shift film 13, and isused to form an opening pattern 13 a in the phase shift film 13. Aresist film (not shown) is provided on the etching mask film 14. In theprocess of manufacturing the reflective mask 2, a first opening patternis first formed in the resist film, a second opening pattern is thenformed in the etching mask film 14 using the first opening pattern, anda third opening pattern 13 a is then formed in the phase shift film 13using the second opening pattern. The first opening pattern, the secondopening pattern, and the third opening pattern 13 a have the samedimensions and the same shape in a plan view (viewed in the Z-axisdirection). The etching mask film 14 enables the resist film to bethinned.

The etching mask film 14 contains at least one element selected from thegroup consisting of aluminum (Al), hafnium (Hf), yttrium (Y), chromium(Cr), niobium (Nb), titanium (Ti), molybdenum (Mo), tantalum (Ta),ruthenium (Ru), and silicon (Si). The etching mask film 14 may containat least one element selected from the group consisting of oxygen (O),nitrogen (N), carbon (C), and boron (B) in addition to theabove-described element. The etching mask film 14 preferably contains atleast one element selected from the group consisting of O, N, and B, andmore preferably contains at least one element selected from the groupconsisting of O and N.

A film thickness of the etching mask film 14 is preferably greater thanor equal to 2 nm and less than or equal to 30 nm, more preferablygreater than or equal to 2 nm and less than or equal to 25 nm, andfurther preferably greater than or equal to 2 nm and less than or equalto 10 nm.

The method of forming the etching mask film 14 includes, for example, aDC sputtering method, a magnetron sputtering method, or an ion beamsputtering method.

Next, a method of manufacturing the reflective mask blank 1 according toone embodiment will be described with reference to FIG. 7 . The methodof manufacturing the reflective mask blank 1 includes, for example,steps S101 to S105 shown in FIG. 7 , i.e., the method includes preparinga substrate 10 (step S101); forming a multilayer reflective film 11 on afirst main surface 10 a of the substrate 10 (step S102); forming aprotection film 12 on the multilayer reflective film 11 (step S103);forming a phase shift film 13 on the protection film 12 (step S104); andforming an etching mask film 14 on the phase shift film 13 (step S105).

The method of manufacturing the reflective mask blank 1 may include atleast steps S101, S102, and S104. The method of manufacturing thereflective mask blank 1 may further include forming a functional film,which is not shown in FIG. 7 . For example, the method of manufacturingthe reflective mask blank 1 may include forming a buffer film 15 betweenthe protection film 12 and the phase shift film 13.

Next, a method of manufacturing the reflective mask 2 according to anembodiment will be described with reference to FIG. 8 . The method ofmanufacturing the reflective mask 2 includes steps S201 to S204 shown inFIG. 8 , i.e., the method includes preparing a reflective mask blank 1(step S201); processing an etching mask film 14, a resist film (notshown) being provided on the etching mask film 14, a first openingpattern being formed in a resist film, and then a second opening patternbeing formed in an etching mask film 14 by using the first openingpattern (step S202); forming a third opening pattern 13 a in a phaseshift film 13 using the second opening pattern, the phase shift film 13being etched using an etching gas (step S203); and removing the resistfilm and the etching mask film 14 (step S204). For removing the resistfilm, for example, a sulfuric acid-hydrogen peroxide mixture is used.For example, an etching gas is used to remove the etching mask film 14.The etching gas used in step S204 (removing the etching mask film 14)may be the same type as the etching gas used in step S203 (forming theopening pattern 13 a). The method of manufacturing the reflective mask 2may include at least steps S201 and S203.

EXAMPLES

Hereinafter, experimental data will be described. Examples 2, 3, 5 to17, 21, 24, and 25 described below are practical examples. Examples 4,18 to 20, 22, and 23 described below are comparative examples. Example 1described below is a reference example.

In Example 1, an EUV mask blank including a substrate, a multilayerreflective film, a protection film, and a phase shift film was prepared.

As the substrate, a SiO₂/TiO₂ glass substrate having a square shape of 6inches (152 mm) per side and a thickness of 6.3 mm was prepared. Theglass substrate had a thermal expansion coefficient at 20° C. of0.02×10⁻⁷/° C., a Young's modulus of 67 GPa, a Poisson's ratio of 0.17,and a specific stiffness of 3.07×10⁷ m²/s². The quality-guaranteedregion of the first main surface of the substrate had a root mean squareroughness Rq of 0.15 nm or less and a flatness of 100 nm or lessobtained by polishing. On the second main surface of the substrate, a Crfilm having a thickness of 100 nm was formed by a magnetron sputteringmethod. The sheet resistance of the Cr film was 100Ω/□.

As the multilayer reflective film, a Mo/Si multilayer reflective filmwas formed. The Mo/Si multilayer reflective film was formed by repeating40 times formation of a Si layer (film thickness: 4.5 nm) and a Mo layer(film thickness: 2.3 nm) by an ion beam sputtering method. A total filmthickness of the Mo/Si multilayer reflective film was 272 nm ((4.5nm+2.3 nm)×40).

As the protection film, a Rh film (film thickness: 2.5 nm) was formed.The Rh film was formed using a DC sputtering method. The reflectance forEUV light by the multilayer reflective film after the protection filmwas formed, that is, the reflectance for the first EUV light L1 shown inFIG. 3 , was 64.5% at the maximum.

In Example 1, a Ru film (film thickness: 32 nm, Ru content: 100 at %)was formed as the phase shift film. The Ru film was formed using a DCsputtering method. The characteristics of the phase shift film will beshown in TABLE 1.

In each of Examples 2 to 25, an EUV mask blank was prepared under thesame condition as in Example 1 except for the chemical composition andthe film thickness of the phase shift film. The characteristics of thephase shift film are shown in TABLE 1. In each of Examples 2 to 25, thephase shift film was an alloy film.

TABLE 1 Etching Composition Optical Film Etching X2 constant thicknessSPM MP1 MP2 Formula Formula rate Material X2 (at %) n k (nm) resistance(° C.) (° C.) (1) (2) CF₄:O₂ (nm/min) Ex. 1 Ru — 0 0.893 0.016 — — 25600 — — — 18 Ex. 2 RuTa Ta 18 0.904 0.019 45 OK 358 509 OK OK 4:28 31Ex. 3 RuTa Ta 46 0.922 0.024 50 OK 876 369 OK OK 8:24 27 Ex. 4 RuTa Ta62 0.932 0.027 56 OK 1172 288 NG NG 8:24 10 Ex. 5 RuW W 20 0.901 0.01942 OK 320 501 OK OK 4:28 35 Ex. 6 RuW W 33 0.906 0.022 42 OK 512 437 OKOK 4:28 26 Ex. 7 RuW W 47 0.912 0.024 47 OK 718 367 OK OK 8:24 24 Ex. 8RuW W 70 0.921 0.028 50 NG 1058 254 OK OK 8:24 26 Ex. 9 RuRe Re 20 0.8950.018 40 OK 100 498 OK NG 4:28 21 Ex. 10 RuRe Re 34 0.897 0.021 42 OK153 427 OK OK 4:28 27 Ex. 11 RuRe Re 45 0.900 0.023 42 OK 194 371 OK OK4:28 42 Ex. 12 RuRe Re 68 0.904 0.028 42 NG 280 253 OK OK 4:28 58 Ex. 13RuCr Cr 6 0.895 0.017 40 OK 163 567 OK NG 4:28 19 Ex. 14 RuCr Cr 140.899 0.019 40 OK 347 524 OK OK 4:28 27 Ex. 15 RuCr Cr 23 0.902 0.021 43OK 553 475 OK OK 4:28 37 Ex. 16 RuCr Cr 41 0.909 0.025 43 OK 966 377 OKOK 4:28 36 Ex. 17 RuHf Hf 11 — — — OK 331 647 OK NG 4:28 20 Ex. 18 RuHfHf 20 — — — OK 580 685 NG NG 8:24 13 Ex. 19 RuHf Hf 29 — — — OK 830 723NG NG 4:28 3 Ex. 20 RuHf Hf 48 — — — OK 1357 804 NG NG 4:28 0 Ex. 21RuAl Al 6 — — — OK 147 699 OK NG 4:28 23 Ex. 22 RuAl Al 20 — — — OK 431930 NG NG — — Ex. 23 RuAl Al 30 — — — OK 634 1095 NG NG — — Ex. 24 RuTaTa 26 0.910 0.021 45 OK 506 469 OK OK 8:24 33 Ex. 25 RuTa Ta 37 0.9170.023 49 OK 710 414 OK OK 8:24 26

In TABLE 1, the melting point MP1 of the oxide of the RuX2 film wascalculated using the following formula (4).

[Equation 5]

MP1=MP1_(A)×(100−a)/100+MP1_(B) ×a/100   (4)

In formula (4), MP1_(A) is a melting point of an oxide of Ru, MP1_(B) isa melting point of an oxide of X2, and a is a content (at %) of X2 inRuX2.

The melting point MP2 of the fluoride or the oxyfluoride of RuX2 shownin TABLE 1 was calculated using the following formula (5).

[Equation 6]

MP2=MP2_(A)×(100−a)/100+MP2_(B) ×a/100   (5)

In formula (5), MP2_(A) is a melting point of a fluoride of Ru, MP2_(B)is a melting point of a fluoride or an oxyfluoride of X2, and a is thecontent (at %) of X2 in RuX2.

TABLE 2 shows an example of the melting point of an oxide of Ru, themelting points of oxides of X2, the melting point of a fluoride of Ru,and the melting points of fluorides or oxyfluorides of X2.

TABLE 2 Oxide Fluoride Oxyfluoride Pure Chemical Melting ChemicalMelting Chemical Melting substance composition point (° C.) compositionpoint (° C.) composition point (° C.) Ru RuO₄ 25.4 RuF₃ 600 — — Ta Ta₂O₅1875 TaF₅ 96.9 — — W WO₂ 1500 — — WOF₄ 105 Re ReO₃ 400 — — ReO₂F₃ 90 CrCr₂O₃ 2320 — — CrOF₄ 55 Hf HfO₂ 2800 HfF₄ 1025 — — Al Al₂O₃ 2054 AlF₃2250 — —

As the melting points shown in TABLE 2, values described in a reference(CRC Handbook of Chemistry and Physics, 93rd Edition) were adopted. Theoxide of each of the pure substances, and the fluoride or oxyfluoride ofeach of the pure substances, shown in TABLE 2, were selected based onknowledge of the inventors of the present application and references onetching.

The melting points MP1 and MP2 shown in TABLE 1 were calculated from thevalues shown in TABLE 2 by using the above formulas (4) and (5). Whenthe Ru compound contains a pure substance, which is not shown in TABLE 2as an element X2, an oxide, and a fluoride or an oxyfluoride of theelement X2 are preferably selected based on references on etching or thelike. When such a reference is not available, a compound of the elementX2 having the lowest valence is preferably selected. The melting pointsMP1 and MP2 are calculated from a melting point of the compound by usingthe above formulas (4) and (5).

Each of the refractive indices n shown in TABLE 1 was calculated, in thesame manner as the melting points MP1 and MP2 shown in TABLE 1, based onthe content a (at %) of X2 in RuX2 and values of the optical constantsof the pure substances described in TABLE 3 shown below.

TABLE 3 Optical constant Pure substance n K Ru 0.8930 0.0160 Ta 0.95670.0343 W 0.9329 0.0329 Re 0.9149 0.0399 Cr 0.9325 0.0389

From TABLE 3, the refractive index of Ru can be found to be low.

In TABLE 1, the SPM resistance of the phase shift film was evaluated andthe etching rate ER of the phase shift film was measured as follows.

The SPM resistance of the phase shift film was evaluated according to anetching rate for the phase shift film in a sulfuric acid-hydrogenperoxide mixture based on a change in a film thickness of the phaseshift film of an EUV mask blank which was immersed in the sulfuricacid-hydrogen peroxide mixture at 100° C. for 20 minutes. The change inthe film thickness of the phase shift film was measured by X-rayreflectometry (XRR). The sulfuric acid-hydrogen peroxide mixture wasprepared by mixing concentrated sulfuric acid and aqueous hydrogenperoxide solution in a ratio of 75 vol %:25 vol %, (concentratedsulfuric acid):(aqueous hydrogen peroxide solution). The concentratedsulfuric acid contained 96 vol % of sulfuric acid and 4 vol % of water.The aqueous hydrogen peroxide solution contained 30 vol %-35 vol % ofhydrogen peroxide and 65 vol %-70 vol % of water. The SPM resistance wasdetermined to be “OK” when the etching rate for the phase shift film inthe sulfuric acid-hydrogen peroxide mixture was 0.05 nm/min or less. TheSPM resistance was determined to be “NG” when the etching rate for thephase shift film in the sulfuric acid-hydrogen peroxide mixture wasgreater than 0.05 nm/min.

The etching rate ER of the phase shift film was obtained by performingan inductively coupled plasma (ICP) etching for the EUV mask blankplaced on a sample stage of an ICP type plasma etching apparatus underthe following conditions.

Conditions of ICP Plasma Etching

ICP antenna bias: 200 W;

Substrate bias: 40 W;

Trigger pressure: 3.5×10⁰ Pa;

Etching pressure: 3.0×10⁻¹ Pa;

Etching gas: mixture gas of an O₂ gas and a CF₄ gas; and

Gas flow rate (CF₄/O₂): 24/8 sccm-4/28 sccm.

As is clear from TABLE 1, in Examples 2, 3, 5 to 17, 21, 24, and 25, themelting points MP1 and MP2 satisfied the formula (1), the etching rateER was greater than that in Example 1, and the processability was betterthan that in Example 1. On the other hand, in Examples 4, 18 to 20, 22,and 23, the melting points MP1 and MP2 did not satisfy the formula (1),the etching rate ER was less than that in Example 1, and theprocessability was worse than that in Example 1.

In addition, as is clear from TABLE 1, in Examples 2, 3, 5 to 8, 10 to12, 14 to 16, 24, and 25, the melting points MP1 and MP2 satisfied boththe formula (1) and the formula (2), the etching rate ER was furthergreater, and the processability was further better.

In Examples 2, 3, 5 to 7, 9 to 11, 14 to 16, 24, and 25, the elementratio between Ta and Ru (Ta:Ru) was 1:99-1:1, the element ratio betweenW and Ru (W:Ru) was 1:99-1:1, the element ratio between Re and Ru(Re:Ru) was 1:99-1:1, or the element ratio between Cr and Ru (Cr:Ru) was1:99-4:1. Therefore, the refractive index was 0.925 or less and the SPMresistance was good.

On the other hand, in Example 8, since the ratio (W/Ru) exceeded 1/1,the SPM resistance was poor. In Example 12, since the ratio (Re/Ru)exceeded 1/1, the SPM resistance was poor.

TABLE 4 shows materials of the protection film or the buffer film. TABLE4 also shows an etching rate ER for each of the materials, and a ratio(selection ratio) of the etching rate ER for RuTa in Example 2 to theetching rate ER for each material.

TABLE 4 Etching rate ER Material (nm/min) Selection ratio Rh 1 31.0 Ru20 1.6 SiO 11 2.8 TaN 1 31.0 TaON 8 3.9 CrN 13 2.4

The etching rate for each material shown in TABLE 4 was measured underthe same condition as the etching rate for RuTa in Example 2. When Rh isused as the material of the protection film, the selection ratio is 10.0or more, and when Ru or SiO is used as the material of the protectionfilm, the selection ratio is less than 10.0. When TaN or TaON is used asthe material of the buffer film, the selection ratio is 3.0 or more, andwhen SiO or CrN is used as the material of the buffer film, theselection ratio is less than 3.0.

As described above, the reflective mask blank, the reflective mask, themethod of manufacturing a reflective mask blank, and the method ofmanufacturing a reflective mask according to the present disclosure havebeen described. However, the present disclosure is not limited to theabove-described embodiments, and the like. Various variations,modifications, substitutions, additions, deletions, and combinations arepossible within the scope of claims. They also of course fall within thetechnical scope of the present disclosure.

1. A reflective mask blank comprising: a substrate; a multilayerreflective film that reflects EUV light; and a phase shift film thatshifts a phase of the EUV light, the substrate, the multilayerreflective film, and the phase shift film being arranged in this order,wherein the phase shift film contains a compound containing Ru and anelement X2 different from Ru, and a melting point MP1 of an oxide of thecompound and a melting point MP2 of a fluoride or an oxyfluoride of thecompound satisfy the following relation (1):0.625 MP1+MP2≤1000   (1).
 2. The reflective mask blank according toclaim 1, wherein the phase shift film contains at least one elementselected from the group consisting of Ta, W, Re, and Cr, as the elementX2.
 3. The reflective mask blank according to claim 2, wherein arefractive index of the phase shift film is 0.925 or less, and anetching rate for the phase shift film with a sulfuric acid-hydrogenperoxide mixture is 0 nm/min to 0.05 nm/min, and in the phase shiftfilm, an element ratio between Ta and Ru (Ta:Ru) is 1:99 to 1:1, anelement ratio between W and Ru (W:Ru) is 1:99 to 1:1, an element ratiobetween Re and Ru (Re:Ru) is 1:99 to 1:1, or an element ratio between Crand Ru (Cr:Ru) is 1:99 to 4:1.
 4. The reflective mask blank according toclaim 3, wherein the element ratio between Ta and Ru (Ta:Ru) in thephase shift film is 1:9 to 1:1.
 5. The reflective mask blank accordingto claim 3, wherein the element ratio between Cr and Ru (Cr:Ru) in thephase shift film is 5:95 to 42:58.
 6. The reflective mask blankaccording to claim 1, wherein the melting point MP1 of the oxide of thecompound and the melting point MP2 of the fluoride or the oxyfluoride ofthe compound satisfy the following relation (2):−0.500 MP1+MP2≤400   (2).
 7. The reflective mask blank according toclaim 1 further comprising: a protection film that protects themultilayer reflective film from an etching gas for etching the phaseshift film, the protection film being arranged between the multilayerreflective film and the phase shift film, wherein a ratio of an etchingrate of etching the phase shift film using the etching gas to an etchingrate of etching the protection film using the etching gas is 10 or more.8. The reflective mask blank according to claim 7, wherein theprotection film contains Rh, or the protection film contains Rh and atleast one element selected from the group consisting of Ru, Si, Al, Hf,Y, Ta, Nb, Mo, and Ir.
 9. The reflective mask blank according to claim 1further comprising: a protection film that protects the multilayerreflective film from an etching gas for etching the phase shift film,the protection film being arranged between the multilayer reflectivefilm and the phase shift film; and a buffer film that protects theprotection film from the etching gas, the buffer film being arrangedbetween the protection film and the phase shift film, wherein a ratio ofan etching rate of etching the phase shift film using the etching gas toan etching rate of etching the buffer film using the etching gas is 3 ormore.
 10. The reflective mask blank according to claim 9, wherein thebuffer film contains Ta, or the buffer film contains Ta and at least oneelement selected from the group consisting of O and N.
 11. Thereflective mask blank according to claim 1 further comprising: anetching mask film on the phase shift film, wherein the etching mask filmcontains at least one element selected from the group consisting of Al,Hf, Y, Cr, Nb, Ti, Mo, Ta, Ru, and Si.
 12. The reflective mask blankaccording to claim 1, wherein the phase shift film further contains, inaddition to Ru and X2, at least one element selected from the groupconsisting of B, C, O, and N.
 13. The reflective mask blank according toclaim 1, wherein the phase shift film contains at least one elementselected from the group consisting of Ta, W, and Re, as the element X2.14. A reflective mask provided with the reflective mask blank accordingto claim 1, wherein the phase shift film includes an opening pattern.15. A method of manufacturing a reflective mask blank, the methodcomprising: forming a multilayer reflective film on a substrate, themultilayer reflective film reflecting EUV light; and forming a phaseshift film over the multilayer reflective film, the phase shift filmshifting a phase of the EUV light, wherein the phase shift film containsa compound containing Ru and an element X2 different from Ru, and amelting point MP1 of an oxide of the compound and a melting point MP2 ofa fluoride or an oxyfluoride of the compound satisfy the followingrelation (1):0.625 MP1+MP2≤1000   (1).
 16. The method of manufacturing a reflectivemask blank according to claim 15, wherein the phase shift film containsat least one element selected from the group consisting of Ta, W, Re,and Cr, as the element X2.
 17. The method of manufacturing a reflectivemask blank according to claim 15, wherein a refractive index of thephase shift film is 0.925 or less, and an etching rate for the phaseshift film with a sulfuric acid-hydrogen peroxide mixture is 0 nm/min to0.05 mm/min, and in the phase shift film, an element ratio between Taand Ru (Ta:Ru) is 1:99 to 1:1, an element ratio between W and Ru (W:Ru)is 1:99 to 1:1, an element ratio between Re and Ru (Re:Ru) is 1:99 to1:1, or an element ratio between Cr and Ru (Cr:Ru) is 1:99 to 4:1.
 18. Amethod of manufacturing a reflective mask, the method comprising:preparing a reflective mask blank manufactured by using the methodaccording to claim 15; and forming an opening pattern in the phase shiftfilm in the reflective mask blank.
 19. The method of manufacturing areflective mask according to claim 18, wherein an etching gas used forforming the opening pattern in the phase shift film is a mixed gas of afluorine-based gas and an oxygen-based gas.
 20. The method ofmanufacturing a reflective mask according to claim 19, wherein thefluorine-based gas is a CF₄ gas, a CHF₃ gas, a SF₆ gas, a BF₃ gas, aXeF₂ gas, or a mixture thereof.
 21. The method of manufacturing areflective mask according to claim 19, wherein a volume ratio betweenthe oxygen-based gas and the fluorine-based gas, (oxygen-basedgas):(fluorine-based gas), is 10:90 to 50:50.